index_file had 3 try/except sites with similar patterns:
Site 3 (BC at L247): try: mtime = os.path.getmtime(full_path); except Exception: return
Site 4 (BC at L261): try: with open(full_path, ...) as f: content = f.read(); except Exception: return
Site 6 (SS at L255): try: res = self.collection.get(...); ...; except Exception: pass
Body: broad catch + early return/pass = SS-style violation.
New helpers:
- _get_file_mtime_result(full_path) -> Result[float]
Catches OSError only (specific to file stat failures).
- _check_existing_index_result(file_path, mtime) -> Result[bool]
Catches broad Exception (chromadb collection.get failures vary).
Returns data=True if already indexed (skip), data=False if needs re-indexing.
- _read_file_content_result(full_path) -> Result[str]
Catches (OSError, UnicodeDecodeError) (file I/O + encoding failures).
Legacy index_file calls each helper; on Result errors, returns early
(preserving the original behavior of skipping the file on failure).
Audit: rag_engine BC 3 -> 1 (L341 _async_search_mcp remaining).
SS: 1 -> 0.
